The Gulf of Mexico and Gulf Coast states have seen a plethora of thunderstorms since about mid-April. One of these episodes was a multi-day event that spanned April 16 – April 20. Multiple rounds of thunderstorms with very heavy rainfall (especially in and around Houston) and some significant severe weather (more hail and wind than tornadoes) traversed the region. The below animation shows these events and I included an example Mesoscale Precipitation Discussion (MPD) from WPC as a reference to the heavy rain.

More recently, on the evening of 04/22/15, a couple strong supercell thunderstorms moved off the Texas coast near the Corpus Christi area and traversed the offshore waters passing relatively close to a couple oil platforms. One of the more amazing attributes to the storms was the strong reflectivities of near 75 dbz! Although these were measured at high altitudes (based on the beam height), it’s interesting to note that large hail may have been occurring well offshore in the Tropical Analysis and Forecast Branch (TAFB) offshore zones. I have included a few animations showing the evolution of these supercells.

National WSR-88D Mosaic base reflectivity with the Overshooting Top Magnitude (OTM) product overlaid highlighting the most intense updrafts associated with the supercells. The OTM product provides the difference between the overshoot and the surrounding cirrus clouds.

National WSR-88D Mosaic base reflectivity overlaid with the GOES-R Lightning Detection (Density) product in 5-minute increments. Note the extreme amount of lightning occurring with the dominant supercells in the Gulf of Mexico.

Here is a post from the National Weather Service Office in Houston-Galveston which nicely summarizes the threat posed to mariners from offshore supercells.

All mariners out there…this is why you should ALWAYS heed a Special Marine Warning. Buoy 42019 measured a 76 kt / 87 mph wind gust at 729 PM associated with this Gulf of Mexico thunderstorm!

The GOES-R Overshooting Top (OT) Detection algorithm (applied to current GOES) was utilized during the very early morning hours of June 23 across the Texas panhandle and western Oklahoma. This algorithm, which automatically detects the location of OT’s using the GOES IR window channel, has proven to be especially valuable in monitoring the evolution of mature convection, especially overnight in the absence of the higher resolution visible imagery. As has been mentioned in previous posts, OT’s indicate the presence of strong updrafts within a convective system, and likely areas of hazardous weather. The algorithm provides forecasters with a tool to quickly spot, in the imagery, where OT’s are present as well as trends in the feature.

By 0400Z on the 23rd, an MCS was propagating across the Texas panhandle/western Oklahoma, producing heavy rainfall and severe winds across the region. An SPC forecaster on shift viewing the OT product utilized it to help monitor trends in the strongest updrafts and areas most likely to be experiencing hazardous weather. The forecaster mentions in a 0723Z SPC Watch Update Mesoscale Discussion (MD,Fig. 1): “TRENDS IN 7 KM AND 9 KM CAPPI AND GOES-R OVERSHOOTING TOP PRODUCT INDICATED THE MORE PERSISTENT UPDRAFTS SINCE AT LEAST 0530z HAVE BEEN FROM THE SRN TX PANHANDLE INTO WRN OK…WITH FORWARD MOVEMENT OF THIS ACTIVITY AT 35-40 KT TOWARD THE SSE.”

Figure 2 is an animation of GOES-East IR imagery with overshooting tops and SPC storm reports overlayed during the time of and in the vicinity of the MD. Notice the cluster of persistent Overshooting Tops within the large cloud shield across the Texas panhandle between 0415 and 0530Z. This is where the highest concentration of severe weather (and heavy rainfall) was reported. Between 0530 and 0730 UTC, the MCS continued to propagate to the SSE as the overshooting tops became more spread out along the leading edge of the system from the southern Texas panhandle into western Oklahoma, as was mentioned in the MD. A few wind reports and heavy rainfall were reported in the vicinity of the persistent OT’s. After 1000Z, the OT’s dropped off completely as the MCS began to weaken.

The storms that ravaged the southern United States this past week not only produced deadly severe weather, but also incredible flooding. Figure 1 shows parts of the Florida Panhandle and southern Alabama received in excess of 10 inches of rain on Tuesday, April 29 alone!

A previous blog post introduced the Overshooting Top Detection product and explained its utility in severe weather situations. Overshooting tops are also indicators of where heavy rainfall may be occurring. Furthermore, the constant presence of overshooting tops over a particular location over an extended period of time may indicate a prolonged period of heavy rainfall, which could lead to flooding.

The animation in Figure 2 shows GOES-East IR imagery with overshooting top detection’s overlaid from the afternoon of the April 29 into the early morning hours of the April 30. During much of this period, GOES-East was in Rapid Scan Mode, meaning images were often available every 5-10 minutes (instead of 15). Notice the persistence of overshooting tops centered over the Mobile area throughout the period, where copious amounts of rainfall were recorded. By about 09Z, a downward trend in overshooting top detection’s had begun as the storm system shifted eastward and weakened. The Overshooting Top Detection product provides a day/night capability for forecasters to easily identify where within a convective system the strongest updrafts are occurring, and where severe weather and/or heavy rainfall may be occurring given other meteorological factors.

Figure 3 shows this same system during the early morning hours of April 30 at much higher resolution. This is a 375 m IR image taken with the Suomi NPP VIIRS instrument. Notice the visibility of features that aren’t easily seen in current GOES IR imagery such as gravity waves and overshooting tops.

Overshooting Tops (OT’s) are domelike bulges atop an anvil cloud that indicate a particularity strong updraft within a convective system that has vertically penetrated the tropopause. Areas of convection possessing OT’s are often associated with hazardous weather at the surface, including lightning, heavy rainfall, and severe weather. An OT Detection (OTD) algorithm has been developed to highlight the presence of overshooting tops, and quantify their strength. This product is especially useful at night in the absence of higher resolution visible imagery and in areas where radar coverage is limited or absent.

The OTD algorithm is currently under evaluation at the Storm Prediction Center (SPC) as part of a GOES-R Proving Ground demonstration. Thus far, SPC forecasters have found this product to be especially useful at night, but also valuable during the daytime. They like that it makes the OT’s stand out, making it easy to observe trends in the feature over several hours. It provides them with additional situational awareness, confirming some of what they may already know in areas of good radar coverage. Finally, forecasters have found it to be useful to monitor trends in OTD’s as a way to monitor mature convective evolution. A persistent OT (or cluster of OT’s) indicates a long-lived strong updraft and storm, while the disappearance of said OT’s over the next few scans is a sign that the updraft is weakening, and the storm may be dissipating.

This final point was on display last night, when an SPC forecaster used the OT product in his decision-making process when issuing an SPC Mesoscale Discussion (http://www.spc.noaa.gov/products/md/md0401.html). He noted “The GOES-R OVERSHOOTING TOP PRODUCT INDICATED A DIMINISHING TREND OVER EAST CENTRAL MS SUCH THAT UPDRAFT INTENSITIES ARE LIKELY WEAKENING”. The animation below shows the IR imagery, storm reports, and OT magnitude with this particular event in NAWIPS.

Notice an OT was first detected with the storm of interest at 0015 UTC in west central Mississippi. This feature was detected by the algorithm over the next several scans (0015-0200 UTC) until 0215, when the OT had collapsed and was no longer detected (as another storm with OTD’s approached from the northwest). The associated storm produced severe winds and large hail at the surface along its path before weakening during the hour after the last scan in which the OT was detected. Particularly large hail (4.25″!) was reported in central Mississippi at 0120 UTC, just after a measured increase was observed in the OT magnitude. This case shows the value in using this product to monitor trends in mature convective evolution and particularly long-lived storms, and how decreasing trends in OTD’s may be a precursor to the dissipation of the convection.

Forecasters will continue to evaluate this product and provide feedback on its operational utility in the SPC. They understand that the algorithm will be much improved and more valuable in the GOES-R era with the increased spatial and temporal resolution of the GOES-R Advanced Baseline Imagery (ABI).

Well, that didn’t take long. . .a week ago we were enduring the wrath of tornadoes through the Plains and Midwest and this week the tropics, not wanting to be out-done, decided to chip in. Tropical Storm Andrea formed late yesterday and has decided to make an early visit to Florida.

I wanted to continue the theme of showing off the capabilities of the Overshooting Top Detection and Lightning Density products that forecasters at the Satellite Proving Ground for Marine, Precipitation, and Hazardous Weather Applications are evaluating. Andrea has put on an interesting show today as you’ll see below.

The Overshooting Top Magnitude Product overlaid on GOES-14 Infrared imagery valid on 06/06/13 (click on image to animate).

The Overshooting Top (OT) Magnitude product (developed by Kris Bedka – SSAI) has been getting quite a workout today over the Gulf and near-shore waters of Florida. Many of the OTs have exhibited a 9-15 degree difference between the OT and the cirrus shield. One OT from early in the loop nearly exceeds the scale I set for the product! Notice how most of the strong OT signatures are seen over water with very few over land in this case. Although wind is expected with a tropical cyclone, these OTs may indicate localized areas of enhanced wind gusts that mariners would have to be made of aware of, even being far from Andrea’s center.

The new experimental GLD-360 Lightning Density product has been very revealing today as it helps to contrast the difference between lighting activity associated with a tropical system and activity associated with continental thunderstorms. Notice how the lighting activity with Andrea starts out relatively quiet, but increases as a squall line develops northwest of Cuba and the Keys. Even so, the lightning activity is not overly impressive as this is 30-minutes of binned lighting strokes. The thunderstorms near the center of Andrea are practically absent of lightning during this entire animation. Meanwhile, the thunderstorms over Louisiana and Texas show very intense lightning activity near the end of the loop.

Pop quiz: why the contrast?

Finally, my email was greeted by some beautiful imagery of Andrea from overnight courtesy of William Straka III from CIMSS at the University of Wisconsin. I have included a couple of these images below for your enjoyment.

Andrea as seen on from the Day-Night Band from VIIRS on the Suomi-NPP satellite valid at 0726 UTC on 06/06/13.

This image from the Day-Night Band on VIIRS is very cool as you are seeing the cloud pattern associated with Andrea with very low amounts of atmospheric light known as “air glow”. The bright spots on the Florida peninsula are the city lights. It’s amazing that even with minimal light, you can still get a feel for the vertical dimensions of the clouds.

Enhanced Infrared imagery from the Suomi-NPP satellite valid at 0726 UTC on 06/06/13.

The last two weeks have featured some rather remarkable weather that has ranged from morning lows around freezing, high temperatures soaring way above 100, and unfortunately, some deadly tornadoes. As part of the Satellite Proving Ground at the NOAA Center for Weather and Climate Prediction (NCWCP), we are currently demonstrating some products that will help with diagnosing and forecasting convection. The Overshooting Top Detection (OTD) is the first product that forecasters are evaluating and in the next few months, we will introduce a new lightning density product (see earlier post on the first spring MCC) that utilizes the Vaisala GLD-360 lightning feed to create a density plot of lightning strikes.

As many of you know, the evening of 05/15 brought some very severe weather to the Dallas-Fort Worth metro with at least one EF-4 and one EF-3 tornado in the southwest suburbs. These storms were part of a larger scale system that was rotating through Oklahoma and the two products mentioned above provided some very interesting and useful information about these storms.

The image above was taken approximately four minutes before the first report of this eventual EF-4 tornado touched down in Granbury, TX. The Overshooting Top Magnitude product adds more information to the overshooting top (OT) associated with this supercell thunderstorm than just the fact that it exists. The OT is approximately 9-11 degrees Celcius colder than the surrounding cirrus of the anvil. This could indicate the potential for large hail and in this case, a precursor to the tornado. Typically, the severe weather occurs between 5-30 minutes after the time of the OT detection.

2 km Mosaic Base Reflective Radar valid at 0104 UTC on 05/16/13.

This radar image compliments the satellite image above and is valid approximately 2 minutes before the tornado report was received. The two supercells highlighted are the tornado producing storms west-northwest of Fort Worth, TX. The southernmost supercell is responsible for the OT seen in the satellite image. Although I cannot say with absolute confidence that the OT Magnitude product would have given a strong indication of a potential EF-4 tornado, it did provide information on the most intense updrafts associated with these storms.

The new Vaisala GLD-360 Lightning Density product that has been developed as a coordinated effort with the Ocean Prediction Center (OPC), NESDIS STAR, and the Cooperative Institute for Climate and Satellites (CICS) did a great job of showing the highest concentration of cloud-to-ground (CG) lightning strikes associated with the thunderstorms about 9 minutes after the tornado report was received. Notice how the two lightning cores are as distinct in this image as the radar image above! This algorithm takes all of the individual CGs (positive and negative) and bins them into 2-minute, 15-minute, and 30-minute lightning density plots. The above image is a 30-minute accumulation of CGs, scaled. The purpose of this product is to simulate the capabilities of the upcoming Geostationary Lightning Mapper (GLM) that will be on GOES-R and is a compliment to the Pseudo-GLM product that is being developed and provided by NASA SPoRT and the University of Alabama-Huntsville.

Another interesting caveat of this severe weather event was this unusually strong OT Magnitude signal observed at 0232 UTC. The OT Magnitude exceeded the scale I created for the product with an OT that was greater than 18 C colder than the surrounding cirrus anvil! I’m sure there was significant hail in this area at this time!

*I created animations of the above mentioned products for this event which you can access at the bottom of this post. Just click on the images and the animation should run on a separate window.*

A Supercell Thunderstorm over the Gulf Stream?!

In the early morning hours of 05/16, another supercell formed nearly 1800 miles to the east-northeast over the Gulf Stream, east of the Mid-Atlantic. As a thunderstorm crossed the north wall of the Gulf Stream, it quickly intensified around 08 UTC into a supercell as it moved east over very warm waters. Although not a threat to anyone, the storm was located over shipping lanes and there was a ship located just northeast of the storm during maximum intensity. As you look at the images below, I want you to think about this question: If you observe similar structures and similar lightning patterns to the TX case, and have no radar, is it possible that this supercell was producing large hail, torrential rainfall, microbursts, or even a large waterspout?

The image above shows the OT Magnitude product indicating an OT that is approximately 16-17 C colder than the surrounding cirrus! This is very intense for a maritime thunderstorm and indicates this storm most likely exhibited a supercell structure. One of the OPC forecasters noted that this is the most intense thunderstorm he has witnessed over the Atlantic offshore zones in a long time.

Once again, the GLD-360 Lightning Density product shows a very intense core of CG lightning strikes co-located with the OT indicated above. It actually appears the lightning was more intense in this supercell than what was observed over TX a few hours earlier.

One of the OPC forecasters had this to say about using these product for his operations:

“I used the overshooting cooling product to help determine the intensity of the supercell, whether [it] was exhibiting a weakening or strengthening trend. In the afternoon I used the overshooting cooling product to support adding higher winds in thunderstorms to the offshore forecast in developing convection over this same offshore zone. The product also validated the very high lightning density data seen with these thunderstorms.”

Once again, I have created animations of this event below for your convenience. Think about the question above when you look at the animations and I encourage you to leave comments or questions as this could lead to interesting discussion. I think these two events provide an interesting comparison and it might be feasible to use these products for maritime convection to warn recreational boaters, military ships, and cargo vessels of potential severe maritime convection. The OPC and Tropical Analysis and Forecast Branch (TAFB) will continue to evaluate these products through the summer as part of the GOES-R Proving Ground activities.

GOES-13 Infrared and OT Magnitude animation valid on 05/16/13. (Click on the image to animate)